This dissertation focuses on the use of novel polyethers and polydimethylsiloxanes in the stabilization of magnetite nanoparticles as well as biomedical applications. The colloidal stabilities of magnetite nanoparticles coated with polyethers containing various functional endgroups were studied. Different variables (e.g. polymer loading, polyether molecular weight and type of functional anchor group) were investigated to determine their effect on the long-term physiological stability of the polyether magnetite complexes. One-part PDMS-magnetite nanoparticle fluids were synthesized using a high shear process and magnetic separation techniques. These one-part fluids are unique in the fact that they do not require the addition of a non-functional PDMS oligomer solvent to generate a magnetic hydrophobic fluid. A series of PDMS-magnetite nanoparticle fluids containing different molecular weight stabilizers were synthesized. A magnetic separation study was performed to determine if PDMS molecular weight influences the magnetic separation profiles of the fluids. Well-defined PDMS-b-PtBA and PDMS-b-poly(acrylic acid) copolymers were synthesized using living free radical techniques from novel PDMS precursors as well as PDMS-based ionenes with different hard segment groups. / Ph. D.

L’objectif de cette thèse était d’étudier suivant deux approches la dégradation des polydiméthylsiloxanes. L’approche expérimentale a permis d’étudier les mécanismes de rupture de chaîne et les phénomènes de réticulation du polymère lorsque ce dernier est soumis à des conditions de thermo-oxydation ou de photo-oxydation comparables à celles du vieillissement naturel. La seconde partie propose de modéliser les résultats expérimentaux par un modèle cinétique issu des calculs ab initio. L’exploitation in vitro de la dégradation du polymère a permis de mettre en évidence la formation de monoxyde de carbone et de dioxyde de carbone, ceux-ci jouant le rôle de révélateurs de rupture de liaison Si-CH3. Toutefois le comportement des PDMS sur des temps de dégradation plus importants montre clairement la formation d’oligomères cycliques par dépolymérisation de la chaîne macromoléculaire. Parallèlement la photo-oxydation de ces polymères entraîne la formation de réseaux multidimensionnels qui traduisent des phénomènes de réticulation avec formation d’acide formique. Cette étude a permis de montrer que la dégradation des PDMS, dans des conditions de vieillissement naturel, procède de deux mécanismes antagonistes, l’un favorisant la réticulation du polymère et le second sa dépolymérisation. La seconde partie de ce travail s’intéresse aux mécanismes de formation des oligomères cycliques observés expérimentalement lors de la dégradation des PDMS. Des réponses précises ont pu être amenées grâce à une analyse théorique détaillée de la constante de cyclisation de ces polymères. Cette étude nous a permis de montrer le rôle essentiel du couplage des rotateurs internes dans le calcul de la constante de cyclisation en fonction de la taille des cycles obtenus. Nos résultats théoriques reproduisent avec exactitude l’évolution de la courbe de la constante de cyclisation observée expérimentalement pour des cycles de taille inférieure à 20 motifs, à savoir un maximum global pour des cycles constitués de quatre motifs et un minimum local pour des cycles à dix motifs. Nous avons démontré que l’origine de l’évolution oscillatoire de la constante de cyclisation traduisait le changement de caractère de certains degrés de liberté entre des vibrations pures (petits cycles) et des rotations empêchées (cycles de plus grande taille). / This work aimed at investigating the degradation pathways of polydimethylsiloxanes through two perspectives. The experimental approach studied bond scission and cross-linking degradation mechanisms when the polymer is exposed to thermo- or photo-oxidation conditions that are similar to that of the natural ageing. In the second part, the experimental results are modeled with a theoretical kinetic model, based on ab initio calculations.The in-vitro study of the polymer degradation showed that formation of carbon monoxide and carbon dioxide were by-products of Si-CH3 bond scissions. However, the degradation of PDMS for longer time periods showed clearly the formation of cyclic oligomers obtained through depolymerization of the macromolecule. In parallel, the photo-oxidation conditions yielded the formation of multidimensional cross-linked networks and formation of formic acid. This study showed that in the natural conditions, the degradation of PDMS proceeded through two opposite mechanisms, one that produced cross-linked networks while in the other, depolymerization was favored. In the second part, we investigated the mechanisms of the formation of cyclic oligomers that were observed experimentally during the degradation of the polymer. A detailed theoretical model was built in order to reproduce the dependence of the experimental cyclization constant with cycle size. This study showed the key role of the coupling in the treatment of hindered rotors. Our theoretical results reproduced accurately the oscillatory behavior of the cyclization constant for cycle sizes less than 20-mers, namely the global maximum for the 4-unit cyclic oligomers, and the local minimum for cycle sizes of 10 units. We have also shown that the origin of the oscillatory behavior of the cyclization constant revealed that some degrees of freedom underwent specific character transformation between a pure vibration for small cycles and hindered rotation for larger ring sizes.

O ácido ƴ-poliglutâmico (ƴ-PGA) é uma homopoliamida aniônica, biodegradável, comestível e atóxica, sintetizada por bactérias do gênero Bacillus, podendo ser utilizado nas indústrias alimentícia e de cosméticos, na medicina e no tratamento de águas residuais. Este trabalho teve como objetivo caracterizar e identificar potenciais aplicações para o ƴ-PGA obtido através do cultivo submerso de Bacillus subtilis BL53, conduzido sob condições otimizadas em trabalhos anteriores. Além disso, foi avaliado o efeito de diferentes inóculos e da adição de precursores da rota metabólica na produção do biopolímero. A melhor condição obtida foi testada em biorreatores com adição de polidimetilsiloxano (PDMS) como carreador de oxigênio, com o objetivo de aumentar a produtividade do biopolímrero. A massa molar média (Mw), obtida através de espalhamento de luz estático, na ordem de 106 g mol-1 não apresentou diferenças significativas para o biopolímero obtido após 48 e 96 h de cultivo. As análises reológicas conduzidas em viscosímetro rotacional indicaram que os polímeros obtidos após 48 e 96 horas apresentaram comportamento Newtoniano, sendo que após 96 horas a viscosidade absoluta foi maior. As análises térmicas (calorimetria diferencial exploratória e análise termogravimétrica) indicaram a temperatura de fusão (Tm) de 134 ºC e 128 ºC e o intervalo de degradação (Td) entre 120 ºC - 190 ºC e 120 ºC - 215 ºC, para os biopolímeros obtidos após 48 e 96 horas de cultivo respectivamente. O caldo LB apresentou-se como o melhor inóculo para a produção de ƴ-PGA. A adição dos precursores L-glutamina e ácido -cetoglutárico aumentou em 20 % a produção do biopolímero. A adição de 10 % de PDMS nos cultivos em biorreatores aumentou o coeficiente volumétrico de transferência de massa (KLa) e a produção e produtividade do ƴ-PGA, sendo produzidos 23.5 g L-1 do biopolímero em 24 horas de cultivo, uma produtividade aproximadamente 40 % superior às obtidas por outros autores utilizando o mesmo microrganismo. / Poly-ƴ-glutamicacid (ƴ-PGA) is an anionic, biodegradable, non-toxic and edible homopolyamide, synthesized by bacteria of the genus Bacillus, being used in food, cosmetics, medicine and waste water treatment. The aim of this study is to characterize and indentify potencial applicatiions for the ƴ-PGA obtained by submerged cultivation of Bacillus subtilis BL53, conducted under optimized conditions in previous studies. We also evaluated the effect of different inoculants and addition of precursors in the metabolic pathway of production of the biopolymer. The best condition obtained yet been tested in bioreactors with addition of polydimethylsiloxane (PDMS) as a carrier of oxygen in order to further increase the productivity of biopolymer. The average molecular weight (Mw) obtained by static light scattering, on the order of 106 g mol-1, showed no significant differences for biopolymer obtained after 48 and 96 h of cultivation. Analyses conducted in rotational viscometer indicated that biopolymers after 48 and 96 h have a Newtonian behavior, and the 96 hours had higher absolute viscosity. The thermal analysis (differential scanning calorimetry and thermo gravimetric analysis) indicated the melting temperature (Tm) as 134 ºC and 128 ºC and degradation temperature range (Td) of 120 ºC - 190 ºC and 120 ºC - 215 ºC, after 48 and 96 hours respectively. It was found that the best inoculum medium for biopolymer production was the LB broth. The addition of the precursors L-glutamine and -ketoglutaric acid increased in 20% the ƴ-PGA production. The addition of 10% of PDMS in bioreactors cultures increased the mass transfer volumetric coefficient (KLa) and the production and productivity of ƴ-PGA, being produced 23.5 g l-1 of the biopolymer in 24 hours of cultivation, a productivity about 40 % higher than those obtained by other authors using the same microorganism.

O ácido ƴ-poliglutâmico (ƴ-PGA) é uma homopoliamida aniônica, biodegradável, comestível e atóxica, sintetizada por bactérias do gênero Bacillus, podendo ser utilizado nas indústrias alimentícia e de cosméticos, na medicina e no tratamento de águas residuais. Este trabalho teve como objetivo caracterizar e identificar potenciais aplicações para o ƴ-PGA obtido através do cultivo submerso de Bacillus subtilis BL53, conduzido sob condições otimizadas em trabalhos anteriores. Além disso, foi avaliado o efeito de diferentes inóculos e da adição de precursores da rota metabólica na produção do biopolímero. A melhor condição obtida foi testada em biorreatores com adição de polidimetilsiloxano (PDMS) como carreador de oxigênio, com o objetivo de aumentar a produtividade do biopolímrero. A massa molar média (Mw), obtida através de espalhamento de luz estático, na ordem de 106 g mol-1 não apresentou diferenças significativas para o biopolímero obtido após 48 e 96 h de cultivo. As análises reológicas conduzidas em viscosímetro rotacional indicaram que os polímeros obtidos após 48 e 96 horas apresentaram comportamento Newtoniano, sendo que após 96 horas a viscosidade absoluta foi maior. As análises térmicas (calorimetria diferencial exploratória e análise termogravimétrica) indicaram a temperatura de fusão (Tm) de 134 ºC e 128 ºC e o intervalo de degradação (Td) entre 120 ºC - 190 ºC e 120 ºC - 215 ºC, para os biopolímeros obtidos após 48 e 96 horas de cultivo respectivamente. O caldo LB apresentou-se como o melhor inóculo para a produção de ƴ-PGA. A adição dos precursores L-glutamina e ácido -cetoglutárico aumentou em 20 % a produção do biopolímero. A adição de 10 % de PDMS nos cultivos em biorreatores aumentou o coeficiente volumétrico de transferência de massa (KLa) e a produção e produtividade do ƴ-PGA, sendo produzidos 23.5 g L-1 do biopolímero em 24 horas de cultivo, uma produtividade aproximadamente 40 % superior às obtidas por outros autores utilizando o mesmo microrganismo. / Poly-ƴ-glutamicacid (ƴ-PGA) is an anionic, biodegradable, non-toxic and edible homopolyamide, synthesized by bacteria of the genus Bacillus, being used in food, cosmetics, medicine and waste water treatment. The aim of this study is to characterize and indentify potencial applicatiions for the ƴ-PGA obtained by submerged cultivation of Bacillus subtilis BL53, conducted under optimized conditions in previous studies. We also evaluated the effect of different inoculants and addition of precursors in the metabolic pathway of production of the biopolymer. The best condition obtained yet been tested in bioreactors with addition of polydimethylsiloxane (PDMS) as a carrier of oxygen in order to further increase the productivity of biopolymer. The average molecular weight (Mw) obtained by static light scattering, on the order of 106 g mol-1, showed no significant differences for biopolymer obtained after 48 and 96 h of cultivation. Analyses conducted in rotational viscometer indicated that biopolymers after 48 and 96 h have a Newtonian behavior, and the 96 hours had higher absolute viscosity. The thermal analysis (differential scanning calorimetry and thermo gravimetric analysis) indicated the melting temperature (Tm) as 134 ºC and 128 ºC and degradation temperature range (Td) of 120 ºC - 190 ºC and 120 ºC - 215 ºC, after 48 and 96 hours respectively. It was found that the best inoculum medium for biopolymer production was the LB broth. The addition of the precursors L-glutamine and -ketoglutaric acid increased in 20% the ƴ-PGA production. The addition of 10% of PDMS in bioreactors cultures increased the mass transfer volumetric coefficient (KLa) and the production and productivity of ƴ-PGA, being produced 23.5 g l-1 of the biopolymer in 24 hours of cultivation, a productivity about 40 % higher than those obtained by other authors using the same microorganism.

O ácido ƴ-poliglutâmico (ƴ-PGA) é uma homopoliamida aniônica, biodegradável, comestível e atóxica, sintetizada por bactérias do gênero Bacillus, podendo ser utilizado nas indústrias alimentícia e de cosméticos, na medicina e no tratamento de águas residuais. Este trabalho teve como objetivo caracterizar e identificar potenciais aplicações para o ƴ-PGA obtido através do cultivo submerso de Bacillus subtilis BL53, conduzido sob condições otimizadas em trabalhos anteriores. Além disso, foi avaliado o efeito de diferentes inóculos e da adição de precursores da rota metabólica na produção do biopolímero. A melhor condição obtida foi testada em biorreatores com adição de polidimetilsiloxano (PDMS) como carreador de oxigênio, com o objetivo de aumentar a produtividade do biopolímrero. A massa molar média (Mw), obtida através de espalhamento de luz estático, na ordem de 106 g mol-1 não apresentou diferenças significativas para o biopolímero obtido após 48 e 96 h de cultivo. As análises reológicas conduzidas em viscosímetro rotacional indicaram que os polímeros obtidos após 48 e 96 horas apresentaram comportamento Newtoniano, sendo que após 96 horas a viscosidade absoluta foi maior. As análises térmicas (calorimetria diferencial exploratória e análise termogravimétrica) indicaram a temperatura de fusão (Tm) de 134 ºC e 128 ºC e o intervalo de degradação (Td) entre 120 ºC - 190 ºC e 120 ºC - 215 ºC, para os biopolímeros obtidos após 48 e 96 horas de cultivo respectivamente. O caldo LB apresentou-se como o melhor inóculo para a produção de ƴ-PGA. A adição dos precursores L-glutamina e ácido -cetoglutárico aumentou em 20 % a produção do biopolímero. A adição de 10 % de PDMS nos cultivos em biorreatores aumentou o coeficiente volumétrico de transferência de massa (KLa) e a produção e produtividade do ƴ-PGA, sendo produzidos 23.5 g L-1 do biopolímero em 24 horas de cultivo, uma produtividade aproximadamente 40 % superior às obtidas por outros autores utilizando o mesmo microrganismo. / Poly-ƴ-glutamicacid (ƴ-PGA) is an anionic, biodegradable, non-toxic and edible homopolyamide, synthesized by bacteria of the genus Bacillus, being used in food, cosmetics, medicine and waste water treatment. The aim of this study is to characterize and indentify potencial applicatiions for the ƴ-PGA obtained by submerged cultivation of Bacillus subtilis BL53, conducted under optimized conditions in previous studies. We also evaluated the effect of different inoculants and addition of precursors in the metabolic pathway of production of the biopolymer. The best condition obtained yet been tested in bioreactors with addition of polydimethylsiloxane (PDMS) as a carrier of oxygen in order to further increase the productivity of biopolymer. The average molecular weight (Mw) obtained by static light scattering, on the order of 106 g mol-1, showed no significant differences for biopolymer obtained after 48 and 96 h of cultivation. Analyses conducted in rotational viscometer indicated that biopolymers after 48 and 96 h have a Newtonian behavior, and the 96 hours had higher absolute viscosity. The thermal analysis (differential scanning calorimetry and thermo gravimetric analysis) indicated the melting temperature (Tm) as 134 ºC and 128 ºC and degradation temperature range (Td) of 120 ºC - 190 ºC and 120 ºC - 215 ºC, after 48 and 96 hours respectively. It was found that the best inoculum medium for biopolymer production was the LB broth. The addition of the precursors L-glutamine and -ketoglutaric acid increased in 20% the ƴ-PGA production. The addition of 10% of PDMS in bioreactors cultures increased the mass transfer volumetric coefficient (KLa) and the production and productivity of ƴ-PGA, being produced 23.5 g l-1 of the biopolymer in 24 hours of cultivation, a productivity about 40 % higher than those obtained by other authors using the same microorganism.

L'objectif de ces travaux de thèse était d'améliorer les performances d'étanchéité de connecteurs automobiles fabriqués en silicone. La première approche visait à comprendre les relations entre les structures chimiques présentes dans les formulations LSR et les propriétés mécaniques afin de proposer des additifs favorisant la résistance à la déchirure. Lors d'une étude préalable, nous avons étudié l'effet synergétique du platine et de la silice sur la dégradation thermique de formulations silicone. Ce travail a permis de décrire le mécanisme et de proposer de nouvelles formulations plus performantes en terme de taux de résidu après pyrolyse. Cette première étude alliée à d'autres techniques a permis d'analyser les structures chimiques présentes dans huit formulations commerciales. Nous avons également caractérisé la réactivité ainsi que la structure du réseau polymère obtenu après réticulation. Les relations liant les structures chimiques à la structure des réseaux ont été établies. Enfin, les propriétés mécaniques telles que la déformation rémanente à la compression, les propriétés ultimes (force et élongation à la rupture) et la résistance à la déchirure des matériaux ont été corrélées avec les différentes structures des réseaux.La seconde partie était dédiée à la synthèse d'un additif fonctionnel thermiquement activable permettant de réparer a posteriori une déchirure. Afin de sélectionner le meilleur système correspondant au cahier des charges, une revue complète de la bibliographie a été réalisée sur la réversibilité des fonctions urées et uréthanes, en portant une attention particulière sur la chimie des isocyanate bloqués. Deux molécules bloquantes ont été sélectionnées après étude de la réactivation thermique de la fonction isocyanate. Un monomère portant cette fonction isocyanate bloqué a été engagé dans une réaction de copolymérisation afin d'obtenir plusieurs générations d'additifs testés selon les normes appliquées aux connecteurs. / This PhD work aimed at improving the water and air-proofing properties of automotive connectors made of silicones. The first approach consisted of understanding the relationships between the chemical structures added in the LSR formulations and their ultimate mechanical performances so as to propose additives which would improve tear resistance of the materials. In a preliminary study, we investigated the synergistic role of platinum catalyst and silica on the thermal degradation of silicone formulations. These investigations allowed us to describe the degradation mechanism and to suggest new formulations in order to improve the residue content at high temperature. This first study, combined with other techniques, allowed us to analyze the chemical structures present in eight commercial formulations. We also characterized the reactivities as well as the network topologies obtained after curing the formulations. Correlations between the chemical structures and the network topology were then established. Finally, some mechanical properties, i.e. the compression set, the ultimate properties (tensile strength and elongation at break) and the tear resistance of final materials were matched with network topologies. The second part was dedicated to the synthesis of a functional additive which could be thermally reactivated to heal a tear. In order to select the best system according to the strict specifications of this work, a complete literature review on the reversibility of urea and urethane bonds was done, with special emphasis on blocked isocyanate chemistry. After a study on the isocyanate group thermal reactivation, two blocking molecules were chosen. A monomer bearing this blocked isocyanate function was then copolymerized to obtain different generations of additives which were finally tested according to standard norms applied to connectors.

Le classement de la famille des dibutylétains par l’Union Européenne comme reprotoxique et mutagène conduit les fabricants d’élastomères silicones à développer des solutions de remplacement de ces composés, largement employés comme catalyseur de réticulation. L’augmentation grandissante de la consommation de ce type d’élastomères amène à s’interroger sur leurs impacts dans les filières de traitement des déchets et sur l’influence du changement de catalyseur sur leur comportement environnemental. Ce domaine de recherche, très peu exploré, demande la mise en place d’une méthodologie spécifique, alliant des expériences de dégradations physico-chimiques et biologiques. Deux types d’élastomères simplifiés, réticulés par trois catalyseurs de polycondensation (un dibutylétain servant de référence et deux nouveaux) sont ciblés comme objet d’étude. Le premier axe, consacré à la matrice silicone, a permis de mettre en évidence une dégradation se déroulant en deux étapes successives, comme lors de la fin de vie de silicones fluides du type PolyDiMéthylSiloxane (PDMS). La première repose sur une hydrolyse chimique des chaînes siloxanes, formant majoritairement des oligosiloxanols (et principalement le monomère diméthylsilanediol) et des méthylsiloxanes cycliques (comme l’octaméthylcyclotétrasiloxane D4). La seconde est une biodégradation des sous-produits d’hydrolyse, aussi bien en aérobiose qu’en anaérobiose. Le second axe, consacré aux catalyseurs de polycondensation, prouve que ces composés prennent une place importante dans les mécanismes de dégradation. Ils impactent principalement les vitesses d’hydrolyse mais peuvent aussi influencer la nature des siloxanes relargués. De plus, ils ont des comportements totalement différents face à la dégradation biologique : ainsi, les catalyseurs organométalliques testés sont assimilables par les micro-organismes comme source primaire de carbone, alors que le catalyseur organique (un dérivé de guanidine) perturbe les métabolismes. Les composés biodégradables, même très peu mobiles en phase aqueuse, sont biodisponibles dans les élastomères et ont un impact sur la diversité des communautés bactériennes. Un champignon du genre Fusarium est d’ailleurs identifié comme capable de métaboliser une des nouvelles molécules développées. Le remplacement des dibutylétains permet de diminuer indiscutablement la toxicité des catalyseurs utilisés dans les élastomères silicones. La méthodologie mise en œuvre apporte de nombreuses informations quant aux impacts environnementaux et pourrait être transposée sans difficulté à l’étude d’autres matériaux. / Dibutyltin compounds are widely used as crosslinking catalysts in silicone elastomer industry. The classification of dibutyltins by the European Union as mutagenic and reprotoxic molecules lead manufacturers of silicone materials to develop alternatives. The increase of silicone elastomers demand requires to study their impacts during waste treatment and to assess the influence of the catalyst change on their environmental behavior. This unexplored area of research requires the establishment of a specific methodology, combining physico-chemical and biological degradation experiments. Two types of simplified elastomers are targeted in this study. They are crosslinked with three polycondensation catalysts: a dibutyltin derivative using as a reference and two new molecules. The first part, devoted to the silicone matrix, demonstrates a two stages degradation pathway in the environment. Silicone elastomers end-of-life is very similar to some silicone fluids, also known as PolyDiMethylSiloxanes (PDMS). The first stage is a chemical hydrolysis of siloxane chains, giving oligosiloxanols (mainly the monomer dimethylsilanediol) and cyclic methylsiloxanes (e.g. octamethylcyclotetrasiloxane D4). The second one is a biodegradation of hydrolysis by-products, in aerobic and anaerobic conditions. The second part, devoted to the polycondensation catalysts, demonstrates that these compounds play an important role in the degradation mechanisms. They mainly impact hydrolysis rates but also affect the nature of released products. In addition, they have a very distinct biological behavior: organometallic catalysts tested are assimilated as a single carbon source by microorganisms, while the organic catalyst (a derivative of guanidine) disrupts bacteria metabolism. Even if they have a limited mobility in the aqueous phase, biodegradable catalysts trapped in the silicone matrix are bioavailable and have an impact on bacterial communities. Moreover, a Fusarium fungus capable of metabolizing one of the new molecules developed is identified. The replacement of dibutyltin compounds undoubtedly reduces the toxicity of catalysts used to synthesized silicone elastomers. The methodology developed provides a lot of information about the environmental impacts of silicone elastomers and could be easily transposed to the study of other materials.